A method is presented for analyzing phonatory instabilities that occur as modulations of fundamental frequency (f0) and sound pressure level (SPL) on the order of 0.2 to 20 cycles per second. Such long-term phonatory instabilities, including but not limited to traditional notions of tremor, are distinct from cycle-to-cycle perturbation such as jitter or shimmer. For each of the 2 parameters (f0, in Hz, and SPL, in dB), 3 frequency domains are proposed: (a) flutter (10–20 Hz), (b) tremor (2–10 Hz), and (c) wow (0.2–2.0 Hz), yielding 6 types of instability. Analyses were implemented using fast Fourier transforms (FFTs) with domain-specific analysis parameters. Outputs include a graphic display in the form of a set of low-frequency spectrograms (the “modulogram”) and quantitative measures of the frequencies, magnitudes, durations, and sinusoidal form of the instabilities. An index of a given instability is developed by combining its duration and average modulation magnitude into a single quantity. Performance of the algorithms was assessed by analyzing test signals with known degrees of modulation, and a range of applications was reviewed to provide a rationale for use of modulograms in phonatory assessment.

Acknowledgments

This work was supported by Grants 5-K08-DC00043-05 and 1-T32-DC00033 from the National Institute on Deafness and Other Communication Disorders (NIDCD). The authors wish also to thank Drs. Michael P. Cannito, Gayle Woodson, and Tom Murry (supported by NIDCD/NIH Grant R15-DC/OD02299-01) for granting access to their recordings of a woman with spasmodic dysphonia. We also wish to extend our gratitude to Sean Iddings, CCC-SLP, Eddie Branch, and Dr. Lesya Chorna for their assistance with development, programming, and testing of the modulogram technique.

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